1. Field of the Invention
The subject invention relates to torsional fluid dampers, methods and apparatus for providing torsional fluid dampening, methods and apparatus for dampening vibrations in elongate information carriers and methods and apparatus for advancing elongate information carriers, such as magnetic recording tapes.
2. Disclosure Statement
In a well-known torsional fluid damper, a flywheel or solid mass is mounted or contained in a tight casing so as to provide small clearances between the solid mass and adjacent wall portions of the casing. The viscous fluid couples the solid mass to the casing and a viscous fluid friction boundary layer is formed therein through rotation of the casing and inertia of the solid mass. By way of example, this type of damper is described in the Shock and Vibration Handbook, by Harris and Crede, pp. 38-30 etc. Reference may, for instance, be had to the Houdaille-type damper shown in FIG. 38.19 of that handbook.
A special type of viscous action damper is shown in U.S. Pat. No. 1,925,690, by L. A. Elmer, wherein fluid is pumped between cylinders and results in a force which, as in all viscous dampers, is proportional to the speed of a rotary container.
That prior-art damper is rather complex and expensive requiring a plurality of pumping cylinder or bellows pairs for its operation.
U.S. Pat. No. 2,280,364, by E. Atteslander, discloses a vibration dampening device in which the center of a hub is filled with lubricating oil through a duct in a supporting shaft. Oil ducts radiate from the center of the hub through arms of a base member to carry lubricating oil to plane contact surfaces of oscillatable members and to friction surfaces of planetary rollers. This prior-art vibration dampening device also is of a complex and expensive construction and shares further disadvantages with the initially mentioned basic torsional fluid damper, including the need for close tolerances which are difficult to establish and maintain.
A vibration dampener for a film advancing apparatus is shown in U.S. Pat. No. 2,819,069, by W. R. Isom. That dampener comprises a relatively rotatable outer flange and an inner cylindrical member. The inside of the cylindrical member contains a silicone oil which may pass through radial holes to an outer recess where it exerts a viscous drag on rotating roller elements. Again, close tolerances are required at the viscous boundary layer for an effective operation of that prior-art drag roller.
U.S. Pat. No. 3,286,109, by E. W. Madsen, discloses a step motor damped by a viscous fluid filling which provides viscous shear between the rotor and the stator of the step motor. This, of course, presupposes that there is in fact a rotor, which requirement necessarily limits the utility of that prior-art device.
U.S. Pat. No. 3,392,953, by J. L. Ciringione et al, discloses a vibration absorber having a cylindrical mass axially supported by a spring rod and immersed in a viscous medium and contained within a light-weight container of slightly larger size. That type of design practically limits the utility of such vibration absorbers to platform stabilization.
U.S. Pat. No. 3,641,839, by A. P. Greeley, discloses a viscous torsional vibration damper of the above mentioned Houdaille type wherein a flywheel or inertia weight has axially facing and circumferential working surfaces in parallel shear film spaced relation to complementary confronting working surfaces of a housing. As with other prior-art dampers of this type, a close tolerance has to be maintained between the flywheel or inertia weight working surfaces and complementary housing working surfaces, in order to establish and maintain efficient coupling shear films of viscous fluid in the spaces or gaps provided between the working surfaces. Special methods and means also have to be provided in these prior-art dampers to assure effective filling of such dampers with the requisite viscous damping media.
Prior-art fluid dampers having an internal solid mass of the above mentioned type are inherently restricted to the sub kHz range as far as oscillation or vibration dampening is concerned. Also, they are inherently incapable of achieving a sufficiently high Q for bandpass functions, whereby undesired vibration or oscillation effects could be selectively eliminated within narrow frequency bands.